A communication scheme succeeding the W-CDMA and the HSDPA, namely, the LTE is discussed by a standardization group 3GPP for the W-CDMA.
As radio access schemes for the LTE, OFDM (Orthogonal Frequency Division Multiplexing) and SC-FDMA (Single-Carrier Frequency Division Multiple Access) are discussed to be used for downlink and uplink, respectively.
The OFDM is a scheme where a certain frequency band is divided into a plurality of narrower frequency bands (subcarriers) and these frequency bands carry data for transmission. According to the OFDM, it is possible to achieve faster transmission and improve frequency utilization efficiency by arranging the subcarriers in the frequency band so densely that the subcarriers can partially overlap one another, without having mutual interference of the subcarriers.
Meanwhile, the SC-FDMA is a transmission scheme where a certain frequency band is divided and thus different frequency bands are used for transmission among multiple mobile stations, so that interference among the multiple mobile stations can be reduced. According to the SC-FDMA, it is possible to achieve low power consumption and wide coverage for the mobile stations since the SC-FDMA is characterized in that transmission power varies to a lesser extent.
Meanwhile, a mobile communication system is a system configured to perform communication by using limited radio resources (frequencies and power) and there is an upper limit on a communication capacity thereof.
Therefore, the number of mobile stations in a cell needs to be restricted in accordance with the above-mentioned communication capacity. For example, there is a case where, when a new mobile station attempts to start communication in the cell, the communication capacity is close to the upper limit because a large number of mobile stations are already performing communication in the cell. In this case, it is necessary to perform control that does not permit the new mobile station to start communication in the cell.
This control is generally referred to as call admission control, or “Call Admission Control (CAC)”.
For example, one of conceivable methods of the call admission control is a method including measuring the number of the mobile stations already performing communication in the cell; giving no permission to the new mobile station to start communication in the cell when the number of the aforementioned mobile stations is more than a predetermined threshold; and giving a permission to the new mobile station to start communication in the cell when the number of the aforementioned mobile stations is equal to or below the predetermined threshold.
Although the above-mentioned example has described the case of using the number of the mobile stations already performing communication in the cell, it is preferable in light of the call admission control to judge whether or not to allow the new mobile station to start communication in the cell, based on an index that represents a degree of congestion in the cell.
Meanwhile, a mobile communication system generally includes multiple carriers. For example, here, assume that a certain mobile communication system has a frequency bandwidth of 20 MHz and the LTE having a system bandwidth of 5 MHz is operated within the frequency bandwidth of 20 MHz. In other words, four LTE carriers are assumed to exist.
In this case, it is preferable in light of effective utilization of frequency resources to equalize degrees of congestion among the four LTE carriers.
Here, one of services offered in the mobile communication system is a real-time service such as “Voice Over IP (VoIP)” or “Streaming”.
In the real-time service, data must be transmitted from a communication source to a communication destination within a predetermined allowable delay due to the nature of the service.
In general, the data in the real-time service are transmitted preferentially over data in a best-effort service in order to satisfy the requirement concerning the delay.
However, in the case of an increase in the number of users performing communication of the real-time service in the cell, it is difficult to satisfy the above-described requirement on the delay for some of the users, because the radio resources in the cell are limited.
Moreover, in light of the call admission control, a phenomenon that there are users under the condition in which the requirement on the delay is not satisfied is used as an index for representing the degree of congestion.
To be more precise, it is conceivable to carry out the call admission control based on the number of users under the condition in which delay time of the real-time service data exceeds a predetermined allowable delay or on the number of the users under the condition in which the real-time service data are discarded in excess of the allowable delay.
However, the above-described conventional mobile communication system has the following problems.
In the mobile communication system of the LTE scheme, the call admission control is executed by a radio base station.
In this case, since a downlink transmission buffer exists in the radio base station, the radio base station can easily monitor discard of packets (data) of a real-time service due to buffered time of the packets in the transmission buffer exceeding the allowable delay.
On the other hand, an uplink transmission buffer exists in the mobile station. Accordingly, the radio base station cannot directly monitor the discard of packets of the real-time service due to the buffered time of the data in the transmission buffer exceeding the allowable delay.
Here, the mobile station is configured to transmit a signal called “Buffer Status Report” to the radio base station in order to notify a transmission buffer state in the mobile station. However, this signal is merely intended for notifying an amount of packets retained in the transmission buffer of the mobile station, and is not intended for notifying the discard of packets due to the buffered time that exceeds the allowable delay.
In the meantime, the mobile station transmits packets on a PDCP layer, while assigning sequence numbers to the packets. Accordingly, a method is also conceivable in which the radio base station estimates the discard of packets due to the buffered time in the transmission buffer of the mobile station exceeding the allowable delay, based on discontinuity of the sequence numbers of the packets on the PDCP layer.
However, an operation of discarding packets before or after the assignment of sequence numbers to the packets on the PDCP layer in the mobile station depends on implementation of the mobile station and is not defined.
To be more precise, the above-mentioned operation of the mobile station is not defined in the Non-patent Document 2 (TS36.323, V8.0.0) to define processing of the PDCP layer.
Therefore, it is difficult to estimate whether or not the packets are discarded in the transmission buffer of the mobile station, based on discontinuity of the sequence numbers.
Accordingly, the present invention has been made in view of the foregoing problems and an object thereof is to provide a mobile station, a radio base station, a communication control method, and a mobile communication system in which, when discarding a packet in a transmission buffer of the mobile station, the radio base station is capable of easily estimating discard of a packet in the transmission buffer of the mobile station, by always assigning a sequence number to the packet and then discarding the packet.
In addition, another object of the present invention is to provide a mobile station, a radio base station, a communication control method, and a mobile communication system which allow: selecting a frequency band to be used for communication or call admission control in a cell; and selecting a frequency band where the mobile station is to camp on after completion of the communication, on the basis of an event reported from the mobile station that the above-mentioned sequence numbers discontinues.
Moreover, still another object of the present invention is to provide a mobile station, a radio base station, a communication control method, and a mobile communication system which allow: monitoring buffered time (a delay amount) of data in an uplink transmission buffer; and reporting to the radio base station an event that the buffered time exceeds a predetermined threshold or an event that data in a transmission buffer of the mobile station are discarded due to excess of an allowable delay.
Further, yet another object of the present invention is to provide a mobile station, a radio base station, a communication control method, and a mobile communication system which allow: selecting the frequency band to be used for communication or call admission control in the cell; and selecting the frequency band where the mobile station is to camp on after completion of the communication, in which, on the basis of the event reported from the mobile station that the buffered time exceeds the predetermined threshold or the event reported from the mobile station that the data in the transmission buffer of the mobile station are discarded due to excess of the allowable delay.
A first aspect of the present invention is summarized as a mobile station configured to transmit and receive a packet provided with a sequence number to and from a radio base station, including: a packet discarder unit configured to discard a packet in an uplink transmission buffer, when a predetermined condition is met; wherein the packet discarder unit is configured to assign a sequence number to the discarded packet.
In the first aspect, the packet discarder unit can be configured to discard the packet, when buffered time of the packet in the transmission buffer exceeds a predetermined threshold.
In the first aspect, the packet discarder unit can be configured to discard the packet for each logical channel or for each logical channel group.
In the first aspect, the uplink transmission buffer can be a buffer for any of a PDCP layer and a RLC layer.
In the first aspect, the packet discarder unit can be configured to assign the sequence number to the discarded packet, by assigning sequence numbers to all packets stored in the transmission buffer.
In the first aspect, the uplink transmission buffer can be a buffer for any of a PDCP layer and a RLC layer; the packet discarder unit can be configured to assign the sequence number to the discarded packet, when a mode of the RLC layer is an unacknowledged mode; and the packet discarder unit can be configured not to assign the sequence number to the discarded packet, when the mode of the RLC layer is an acknowledged mode.
A second aspect of the present invention is summarized as a radio base station configured to transmit and receive a packet provided with a sequence number to and from a mobile station, including: a call admission controller unit configured to control admission of communication by a new mobile station, based on discontinuity of sequence numbers of packets received on an uplink.
A third aspect of the present invention is summarized as a radio base station configured to transmit and receive a packet provided with a sequence number to and from a mobile station, including: a discontinuity detector unit configured to detect discontinuity of sequence packets of a signal received on an uplink; a calculator unit configured to calculate any of the numbers of mobile stations and logical channels each incurring discontinuity of sequence numbers of the packets; and a call admission controller unit configured to control admission of communication by a new mobile station, based on any of the numbers of the mobile stations and the logical channels each incurring the discontinuity of the sequence numbers.
A fourth aspect of the present invention is summarized as a radio base station configured to transmit and receive a packet provided with a sequence number to and from a mobile station, including: a discontinuity detector unit configured to detect discontinuity of sequence numbers of packets received on an uplink; a calculator unit configured to calculate any of the numbers of mobile stations and logical channels each incurring discontinuity of sequence numbers of the packets; and a frequency band selector unit configured to select a frequency band to be used by a mobile station newly performing communication, based on any of the numbers of the mobile stations and the logical channels each incurring the discontinuity of the sequence numbers.
A fifth aspect of the present invention is summarized as a radio base station configured to transmit and receive a packet provided with a sequence number to and from a mobile station, including: a discontinuity detector unit configured to detect discontinuity of sequence numbers of packets received on an uplink; a calculator unit configured to calculate any of the numbers of mobile stations and logical channels each incurring discontinuity of sequence numbers of the packets; and a frequency band selector unit configured to select a frequency band in which a mobile station having completed communication is to camp on, based on any of the numbers of the mobile stations and the logical channels each incurring the discontinuity of the sequence numbers.
A sixth aspect of the present invention is summarized as a communication control method in a mobile station configured to transmit and receive a packet provided with a sequence number to and from a radio base station, including the step of: discarding a packet in an uplink transmission buffer, when a predetermined condition is met; wherein the discarded packet
A seventh aspect of the present invention is summarized as a communication control method in a radio base station configured to transmit and receive a packet provided with a sequence number to and from a mobile station, including the steps of: detecting discontinuity of sequence numbers of packets received on an uplink; calculating any of the numbers of mobile stations and logical channels each incurring discontinuity of sequence numbers of the packets; and controlling admission of communication by a new mobile station, based on any of the numbers of the mobile stations and the logical channels.
An eighth aspect of the present invention is summarized as a mobile communication system including: a plurality of mobile stations; a radio base station configured to perform communication with the plurality of mobile stations by using a shared channel; a data server configured to save data transmitted from the radio base station; and a monitor terminal to which the data saved in the data server are outputted; wherein each of the plurality of mobile stations includes a packet discarder unit configured to assign a sequence number to a packet in an uplink transmission buffer and to discard the packet when a predetermined condition is met, the radio base station includes: a discontinuity detector unit configured to detect discontinuity of sequence numbers of packets received on an uplink from the plurality of mobile stations; a calculator unit configured to calculate any of the numbers of mobile stations and logical channels each incurring discontinuity of sequence numbers of the packets; and a reporter unit configured to report any of the numbers of the mobile stations and the logical channels to the data server; and the data server includes: a saver unit configured to save any of the numbers of the mobile stations and the logical channels as a statistical value; and an output unit configured to output any of the numbers of the mobile stations and the logical channels to the monitor terminal.
A ninth aspect of the present invention is summarized as a mobile station configured to perform communication with a radio base station, including: a data discarder unit configured to discard data in an uplink transmission buffer, when a predetermined condition is met; and a reporter unit configured to report discard of the data to the radio base station.
In the ninth aspect, the data discarder unit can be configured to discard the data, when buffered time of the data in the transmission buffer exceeds a predetermined threshold.
In the ninth aspect, the reporter unit can be configured to report the discard of the data by use of a measurement report for reporting a measurement result of communication quality on a downlink.
In the ninth aspect, the reporter unit can be configured to report the discard of the data, when any of the number of times of discard of the data and a discard proportion of the data exceeds a predetermined threshold.
In the ninth aspect, the reporter unit can be configured to report the discard of the data in response to an instruction from the radio base station.
In the ninth aspect, the data discarder unit can be configured to discard the data for each logical channel or each logical channel group; and the reporter unit can be configured to report the discard of the data for each logical channel or each logical channel group.
In the ninth aspect, the uplink transmission buffer can be a buffer for any of a PDCP layer and a RLC layer.
A tenth aspect of the present invention is summarized as a radio base station configured to perform communication with a mobile station, including: an instructor unit configured to instruct the mobile station to report discard of data in an uplink transmission buffer; and
a receiver unit configured to receive a report of the discard of the data in the uplink transmission buffer from the mobile station.
An eleventh aspect of the present invention is summarized as a radio base station configured to perform communication with a plurality of mobile stations, including: an instructor unit configured to instruct the plurality of mobile stations to report discard of data in uplink transmission buffers; a receiver unit configured to receive reports of the discard of the data in the uplink transmission buffers from the plurality of mobile stations; a calculator unit configured to calculate any of the numbers of the mobile stations and logical channels each incurring the discard of the data; and a call admission controller unit configured to control admission of communication by a new mobile station, based on any of the numbers of the mobile stations and the logical channels.
A twelfth aspect of the present invention is summarized as a radio base station configured to perform communication with a plurality of mobile stations, including: an instructor unit configured to instruct the plurality of mobile stations to report discard of data in uplink transmission buffers; a receiver unit configured to receive reports of the discard of the data in the uplink transmission buffers from the plurality of mobile stations; a calculator unit configured to calculate any of the numbers of the mobile stations and logical channels each incurring the discard of the data; and a frequency band selector unit configured to select a frequency band to be used by a mobile station newly performing communication, based on any of the numbers of the mobile stations and the logical channels.
A thirteenth aspect of the present invention is summarized as a radio base station configured to perform communication with a plurality of mobile stations, including: an instructor unit configured to instruct the plurality of mobile stations to report discard of data in uplink transmission buffers; a receiver unit configured to receive reports of the discard of the data in the uplink transmission buffers from the plurality of mobile stations; a calculator unit configured to calculate any of the numbers of the mobile stations and logical channels each incurring the discard of the data; and a frequency band selector unit configured to select a frequency band in which a mobile station having completed communication is to camp on, based on any of the numbers of the mobile stations and the logical channels.
A fourteenth aspect of the present invention is summarized as a communication control method in a mobile station configured to perform communication with a radio base station, including the steps of: discarding data in an uplink transmission buffer when a predetermined condition is met; and reporting discard of the data to the radio base station.
A fifteenth aspect of the present invention is summarized as a communication control method in a radio base station configured to perform communication with a plurality of mobile stations, including the steps of: instructing the plurality of mobile stations to report discard of data in uplink transmission buffers; receiving reports of the discard of the data in the uplink transmission buffers from the plurality of mobile stations; calculating any of the numbers of the mobile stations and logical channels each incurring the discard of the data; and controlling admission of communication by a new mobile station, based on any of the numbers of the mobile stations and the logical channels.
A sixteenth aspect of the present invention is summarized as a mobile communication system including: a plurality of mobile stations; a radio base station configured to perform communication with the plurality of mobile stations by using a shared channel; a data server configured to save data transmitted from the radio base station; and a monitor terminal to which the data saved in the data server are outputted; wherein each of the plurality of mobile stations includes: a data discarder unit configured to discard data in a uplink transmission buffer, when a predetermined condition is met; and a reporter unit configured to report discard of the data to the radio base station, the radio base station includes: a receiver unit configured to receive reports of the discard of the data in the uplink transmission buffers from the plurality of mobile stations; a calculator unit configured to calculate any of the numbers of the mobile stations and logical channels each incurring the discard of the data; and a reporter unit configured to report any of the numbers of the mobile stations and the logical channels to the data server; and the data server includes: a saver unit configured to save any of the numbers of the mobile stations and the logical channels as a statistical value; and an output unit configured to output any of the numbers of the mobile stations and the logical channels to the monitor terminal.
A seventeenth aspect of the present invention is summarized as a mobile station configured to perform communication with a radio base station, including: a calculator unit configured to calculate average time from generation to transmission of data in an uplink transmission buffer; and a reporter unit configured to report that the average time exceeds a predetermined threshold, or to report the average time to the radio base station when the average time exceeds the predetermined threshold.